The present invention relates generally to an image-formation lens, and an imaging system incorporating the same, and particularly to a zoom lens system having a zooming action. More particularly, the present invention is concerned with an inexpensive, small-format, high-zoom-ratio zoom lens system that is well fit for phototaking lenses for, e.g., lens shutter cameras or digital cameras.
Various arrangements such as two-group arrangements comprising a positive front group and a negative rear group, and three-group arrangements comprising a positive first lens group, a positive second lens group and a negative third lens group have so far been proposed for inexpensive, small-format, high-zoom-ratio zoom lenses used on lens shutter cameras.
For instance, Patent Publication 1 proposes a two-group zoom lens of +− construction, and Patent Publications 2–4 put forward a three-group zoom lens of ++− construction, which comprises up to 10 lenses. All these zoom lenses are relatively inexpensive and have a high zoom ratio.
Patent Publication 1                JP-A 9-90220        
Patent Publication 2                JP-A 2000-21802        
Patent Publication 3                JP-A 2000-275524        
Patent Publication 4                JP-A 2000-19399        
In such conventional zoom lenses, however, there is still much left to be desired in terms of performance, size and cost.